I would like to get statistics on the use of site-specific off-topic subreasons and to see what kinds of free-form reasons have been used. How can I do that? As far as I can tell this is still not possible.

The API allows me to search for closed questions, and gives the close reason, but only returns undifferentiated comments, so I can't automatically select subreason. This only tells me about questions that have been closed, too.

The data explorer is now updated often and includes all sites. However, for close votes, it only gives the information that “off-topic” was used, it doesn't give any information about moderator-chosen or write-in subreasons. Moderaton-chosen reasons are recorded in the PendingFlags column but that doesn't help for close votes and flags that are no longer pending.

Please provide a way to retrieve a list of off-topic subreasons that have been used, and whether they resulted in closure or not.